Scintillation crystal, a radiation detection system including the scintillation crystal, and a method of using the radiation detection system

ABSTRACT

A scintillation crystal can include Ln (1-y) RE y X 3 , wherein Ln represents a rare earth element, RE represents a different rare earth element, y has a value in a range of 0 to 1, and X represents a halogen. In an embodiment, RE is Ce, and the scintillation crystal is doped with Sr, Ba, or a mixture thereof at a concentration of at least approximately 0.0002 wt. %. In another embodiment, the scintillation crystal can have unexpectedly improved linearity and unexpectedly improved energy resolution properties. In a further embodiment, a radiation detection system can include the scintillation crystal, a photosensor, and an electronics device. Such a radiation detection system can be useful in a variety of radiation imaging applications.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority under 35U.S.C. § 120 to U.S. patent application Ser. No. 15/710,509, entitled“Scintillation Crystal, a Radiation Detection System Including theScintillation Crystal, and a Method of Using the Radiation DetectionSystem,” by Menge et al, filed Sep. 20, 2017, which is a continuation ofand claims priority under 35 U.S.C § 120 to U.S. patent application Ser.No. 14/966,610 entitled “Method of Forming a Scintillation CrystalIncluding a Rare Earth Halide,” by Menge et al., filed Dec. 11, 2015,now U.S. Pat. No. 9,796,922, which is a continuation of and claimspriority under 35 U.S.C. § 120 to U.S. patent application Ser. No.13/488,756 entitled “Scintillation Crystal Including a Rare EarthHalide, and a Radiation Detection System Including the ScintillationCrystal,” by Menge et al., filed Jun. 5, 2012, which is anon-provisional application that claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/493,805 entitled“Scintillation Crystal Including a Rare Earth Halide, and a RadiationDetection System Including the Scintillation Crystal,” by Menge et al.,filed Jun. 6, 2011, all of which are assigned to the current assigneehereof and incorporated herein by reference in their entireties.

FIELD OF THE DISCLOSURE

The present disclosure is directed to scintillation crystals includingrare earth halides and radiation detection systems including suchscintillation crystals.

BACKGROUND

Radiation detection systems are used in a variety of applications. Forexample, scintillators can be used for medical imaging and for welllogging in the oil and gas industry as well for the environmentmonitoring, security applications, and for nuclear physics analysis andapplications. Scintillation crystals used for radiation detectionsystems can include rare earth halides. Further improvement ofscintillation crystals is desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited in theaccompanying figures.

FIG. 1 includes an illustration of a radiation detection system inaccordance with an embodiment.

FIG. 2 includes an illustration of departure from perfect linearity fordifferent compositions of scintillation crystals at gamma ray energiesin a range of approximately 200 keV to approximately 2600 keV.

FIG. 3 includes an illustration of departure from perfect linearity fordifferent compositions of scintillation crystals at gamma ray energiesin a range of approximately 60 keV to approximately 356 keV.

FIG. 4 includes a plot of energy resolution as a function of energy fora Sr-doped scintillation crystal, a Zn-doped scintillation crystal, anda standard scintillation crystal

FIG. 5 includes a plot of energy resolution ratio as a function ofenergy for a Sr-doped scintillation crystal, a Zn-doped scintillationcrystal, and a standard scintillation crystal

FIG. 6 includes an emission spectrum for a Sr-doped scintillationcrystal, a Zn-doped scintillation crystal, and a standard scintillationcrystal.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures maybe exaggerated relative to other elements to help to improveunderstanding of embodiments of the invention.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

The term “averaged,” when referring to a value, is intended to mean anaverage, a geometric mean, or a median value.

The term “corresponding undoped scintillation crystal” is intended tomean a particular scintillation crystal that includes the samehalogen(s) and rare earth element(s) in substantially the sameproportions as a doped scintillation crystal to which such particularscintillation crystal is being compared. For example, a dopedscintillation crystal that includes a Sr-doped La1.9Ce0.1Br3 has acorresponding undoped scintillating crystal of La1.9Ce0.1Br3. Note thateach of the doped and corresponding undoped scintillation crystals havetrace levels of detectable impurities; however, the correspondingundoped scintillation crystal does not include a dopant that is addedseparately when forming the scintillation crystal.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

The use of “a” or “an” is employed to describe elements and componentsdescribed herein. This is done merely for convenience and to give ageneral sense of the scope of the invention. This description should beread to include one or at least one and the singular also includes theplural, or vice versa, unless it is clear that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in textbooks andother sources within the scintillation and radiation detection arts.

FIG. 1 illustrates an embodiment of a radiation detector system 100. Theradiation detector system can be a medical imaging apparatus, a welllogging apparatus, a security inspection apparatus, nuclear physicsapplications, or the like. In a particular embodiment, the radiationdetection system can be used for gamma ray analysis, such as a SinglePositron Emission Computer Tomography (SPECT) or Positron EmissionTomography (PET) analysis.

In the embodiment illustrated, the radiation detection system 100includes a photosensor 101, an optical interface 103, and ascintillation device 105. Although the photosensor 101, the opticalinterface 103, and the scintillation device 105 are illustrated separatefrom each other, skilled artisans will appreciate that photosensor 101and the scintillation device 105 can be coupled to the optical interface103, with the optical interface 103 disposed between the photosensor 101and the scintillation device 105. The scintillation device 105 and thephotosensor 101 can be optically coupled to the optical interface 103with other known coupling methods, such as the use of an optical gel orbonding agent, or directly through molecular adhesion of opticallycoupled elements.

The photosensor 101 may be a photomultiplier tube (PMT), asemiconductor-based photomultiplier, or a hybrid photosensor. Thephotosensor 101 can receive photons emitted by the scintillation device105, via an input window 116, and produce electrical pulses based onnumbers of photons that it receives. The photosensor 101 is electricallycoupled to an electronics module 130. The electrical pulses can beshaped, digitized, analyzed, or any combination thereof by theelectronics module 130 to provide a count of the photons received at thephotosensor 101 or other information. The electronics module 130 caninclude an amplifier, a pre-amplifier, a discriminator, ananalog-to-digital signal converter, a photon counter, another electroniccomponent, or any combination thereof. The photosensor 101 can be housedwithin a tube or housing made of a material capable of protecting thephotosensor 101, the electronics module 130, or a combination thereof,such as a metal, metal alloy, other material, or any combinationthereof.

The scintillation device 105 includes a scintillation crystal 107. Thecomposition of the scintillation crystal 107 will be described in moredetail later in this specification. The scintillation crystal 107 issubstantially surrounded by a reflector 109. In one embodiment, thereflector 109 can include polytetrafluoroethylene (PTFE), anothermaterial adapted to reflect light emitted by the scintillation crystal107, or a combination thereof. In an illustrative embodiment, thereflector 109 can be substantially surrounded by a shock absorbingmember 111. The scintillation crystal 107, the reflector 109, and theshock absorbing member 111 can be housed within a casing 113.

The scintillation device 105 includes at least one stabilizationmechanism adapted to reduce relative movement between the scintillationcrystal 107 and other elements of the radiation detection system 100,such as the optical interface 103, the casing 113, the shock absorbingmember 111, the reflector 109, or any combination thereof. Thestabilization mechanism may include a spring 119, an elastomer, anothersuitable stabilization mechanism, or a combination thereof. Thestabilization mechanism can be adapted to apply lateral forces,horizontal forces, or a combination thereof, to the scintillationcrystal 107 to stabilize its position relative to one or more otherelements of the radiation detection system 100.

As illustrated, the optical interface 103 is adapted to be coupledbetween the photosensor 101 and the scintillation device 105. Theoptical interface 103 is also adapted to facilitate optical couplingbetween the photosensor 101 and the scintillation device 105. Theoptical interface 103 can include a polymer, such as a silicone rubber,that is polarized to align the reflective indices of the scintillationcrystal 107 and the input window 116. In other embodiments, the opticalinterface 103 can include gels or colloids that include polymers andadditional elements.

The scintillation crystal 107 can include a rare earth halide. As usedherein, rare earth elements include Y, Sc, and the Lanthanide serieselements. In an embodiment, the scintillation crystal 107 can includeone or more other rare earth elements. Thus, the scintillation crystal107 can have chemical formula as set forth below.

Ln(1−y)REyX3, wherein:

Ln represents a rare earth element;

RE represents a different rare earth element;

y has a value in a range of 0 to 1 formula unit (“f.u.”); and

X represents a halogen.

In particular embodiment, Ln can include La, Gd, Lu, or any mixturethereof; and RE can include Ce, Eu, Pr, Tb, Nd, or any mixture thereof.In a particular embodiment, the scintillation crystal 107 can beLa(1−y)CeyBr3. In particular embodiments, LaBr3 and CeBr3 are within thescope of compositions described.

In another a further embodiment y can be 0 f.u., at least approximately0.0001 f.u., at least 0.001 f.u., or at least approximately 0.05 f.u. Ina further embodiment, y may be 1 f.u., no greater than approximately 0.2f.u., no greater than approximately 0.1 f.u., no greater thanapproximately 0.05 f.u, or no greater than approximately 0.01 f.u. In aparticular embodiment, y is in a range of approximately 0.01 f.u. toapproximately 0.1 f.u. X can include a single halogen or any mixture ofhalogens. For example, X can include Br, I, or any mixture thereof.

The rare earth halide can further include Sr, Ba, or any mixturethereof. In an embodiment, the content of Sr, Ba, or any mixture thereofin the scintillation crystal can be at least approximately 0.0002 wt. %,at least approximately 0.0005 wt. %, or at least approximately 0.001 wt.%. In another embodiment, the content of Sr, Ba, or any mixture thereofin the scintillation crystal may be no greater than approximately 0.05wt. %, no greater than approximately 0.03 wt. %, no greater than 0.02wt. %, or no greater than approximately 0.009 wt. %. In a particularembodiment, the content of Sr, Ba, or any mixture thereof is in a rangeapproximately 0.005 wt. % to approximately 0.02 wt. %

The starting materials can include metal halides of the same halogen ordifferent halogens. For example, a rare earth bromide and SrBr2 can beused. In another embodiment, some of the bromide-containing compoundsmay be replaced with iodide-containing compounds. The starting materialsmay be selected such that a principal rare earth halide and anothermetal halide for the scintillation crystal have melting points withapproximately 90° C. of each other. In a particular embodiment, meltingpoints with approximately 50° C. of each other. For example, LaBr3 has amelting point of approximately 785° C., and SrBr2 has a melting point ofapproximately 640° C. When the melting points are closer to each other,more of the dopant may be incorporated into the scintillation crystal,if needed or desired. In another embodiment, BaBr2 or any mixture ofSrBr2 and BaBr2 can be used.

The scintillation crystal can be formed using a conventional techniquefrom a melt. The method can include the Bridgman method or Czochralskicrystal growth method.

Scintillation crystals that include a Sr-doped, Ba-doped, or Sr and Baco-doped rare earth halide provide unexpected results as compared toother rare earth halide scintillation crystals. More particularly, theSr-doped, Ba-doped, or Sr and Ba co-doped scintillation crystals haveunusually good linearity, an unusually good energy resolution, and alower bandgap energy.

Linearity refers to how well a scintillation crystal approaches perfectlinear proportionality between gamma ray energy and light output. Thelinearity can be measured as a departure from perfect linearity. Ascintillation crystal having perfect linearity would always create thesame number of photons per unit energy absorbed, regardless of theenergy of the gamma ray. Thus, its departure from perfect linearity iszero. The departure from perfect linearity between different rare earthhalides is more significant at lower energies than it is for higherenergies. A higher energy gamma ray (for example, greater than 2000 keV)may hit the scintillation crystal, which in turn, may generate lowerenergy gamma rays (for example, less than 300 keV). If the scintillationcrystal generates less scintillating light for lower energy gamma rays,the scintillation crystal has poor linearity. Thus, the response of thescintillation crystal to gamma rays at lower energies, such as less than300 keV, can be more significant to linearity than the response athigher gamma ray energies.

Departure from perfect linearity can be determined as follows. Data forresponses to different gamma ray energies are collected over a range ofgamma ray energies. For example, the range of gamma ray energies can befrom 60 keV to 6130 keV. The range may be narrower, for example, 60 keVto 2600 keV. The lower limit on the range may be different from 60 keV.The lower limit for the range may be less than 60 keV (for example 20keV or 40 keV) or higher than 60 keV (for example 100 or 200 keV). Afterreading this specification, skilled artisans will be able to select anenergy range for their particular application.

After the data is collected, using a least squares fit, a linearequation is generated having an equation of:Ecalc=m*PH  Equation 1

where:

Ecalc is the calculated energy;

PH is the pulse height (light output); and

m is the slope of the line (fit coefficient).

Note that the line passes through the point (0,0) corresponding to apulse height of zero (no light output) when the energy is zero. Thus,there is no y-axis offset when the line corresponds to perfectlinearity. For a particular gamma ray energy, the deviation from perfectlinearity (“DFPL”) is determined by the following equation.DFPL=((Ecalc−Eactual)/Eactual)*100%  Equation 2

where Eactual is the actual gamma ray energy corresponding to lightoutput and Ecalc is calculated using the light output.

For a set of DFPL data points, an averaged value, a largest positivedeviation, a largest negative deviation, a maximum deviation, anabsolute value of any of the foregoing, or any combination thereof canbe obtained. The averaged value can be an average, a median, or ageometric mean. In a particular embodiment, the average DFPL can bedetermined using an integral in accordance with Equation 3 below.

$\begin{matrix}{{DFPLaverage} = \frac{\int\limits_{E_{lower}}^{E_{upper}}{{{DFPL}\left( E_{i} \right)} \cdot {dE}_{i}}}{E_{upper} - E_{lower}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where

DFPL(Ei) is DFPL at energy Ei;

Eupper is the upper limit of the energy range; and

Elower is the lower limit of the energy range.

For a radiation energy range from 60 keV to 356 keV, the rare earthhalide scintillator crystal can have an averaged value for a departurefrom perfect linearity of no less than approximately −0.35%, no lessthan approximately −0.30%, or no less than approximately −0.25%, no lessthan approximately −0.20%, or no less than approximately −0.16%. For aradiation energy range of 2000 keV to 2600 keV, the averaged value for adeparture from perfect linearity may be based on absolute values becausethe departure from perfect linearity may cross 0.00% within theradiation energy ranges. Accordingly, for a radiation energy range of2000 keV to 2600 keV, the rare earth scintillation crystal has anaveraged value for a departure from perfect linearity, based on absolutevalues of no greater than approximately 0.07%, no greater thanapproximately 0.05%, or no greater than approximately 0.03%.

In a particular embodiment, the averaged values can be DFPLaverage(Equation 3) as described above. For a radiation energy range from 60keV to 356 keV, the rare earth halide scintillation crystal has anabsolute value for a furthest departure from perfect linearity of nogreater than approximately 0.70%, no greater than approximately 0.65%,no greater than approximately 0.65% no greater than approximately 0.60%no greater than approximately 0.55%, or no greater than approximately0.50%.

The scintillation crystal can also have unexpectedly good energyresolution properties, such as energy resolution, energy resolutionratio, and potentially other related properties. In the paragraphsbelow, energy resolution and energy resolution ratio are addressed inmore detail.

Energy resolution is the energy range at full-width of half maximum(“FWHM”) divided by the energy corresponding to the peak, expressed as apercent. A lower number for energy resolution means that the peak can beresolved more readily. Values for energy resolution may depend on thesample, the metrology equipment, and the measurement techniques. In anembodiment, measurements for energy resolution may be performed onscintillation crystals that are right circular cylinders with diameterof approximately 64 mm (2.5 inches) and length of approximately 75 mm (3inches). In a particular embodiment, the sides and one circular face maybe roughened to a root-mean-square roughness of 0.85 microns, and inanother particular embodiment, the other circular face of each crystalmay be polished and serve as the optical exit for scintillation light.In another embodiment, the crystals can be wrapped with a reflector onthe sides and one end. In a particular embodiment, the reflector may bea specular reflector or a diffuse reflector. For example, the reflectormay include an aluminum foil, aluminized polyester (e.g. aluminizedMylar™-brand polyester), or a polytetrafluoroethylene (“PTFE”) sheetreflector. In another embodiment, the scintillation crystal can beplaced in a housing where scintillating light passes through a sapphireor quartz window.

The housed scintillation crystal can be interfaced to a photomultipliertube. In an embodiment, the photomultiplier tube can be a linearlyfocused, non-saturated photomultiplier. By non-saturated, thephotomultiplier operates in a mode in which significantly more electronsmay be generated with a significantly higher rate of photons strikingthe photocathode of the photomultiplier tube. An exemplaryphotomultiplier can be obtained from ET Enterprises Ltd. of Uxbridge,U.K., model 9305 run at 900 V. One or more desired isotopes can beplaced one at a time at a distance of approximately 150 mm (6 inches)from each crystal package's midplane. The energy spectra of each isotopeand each crystal can be obtained from a multi-channel analyzer thatperforms bi-polar shaping at a 0.25 micro-s shaping time. An exemplarymultichannel analyzer can be obtained from Canberra Industries Inc. ofMeriden Conn., model Aptec S5008 that has bi-polar shaping, 0.25 micro-sshaping time, and 11-bit digitization.

After reading this specification, skilled artisans will appreciate thatthe energy resolution values that they obtain may change if the samplepreparation, metrology equipment, and the measurement techniques arechanged. The energy resolution values described below can be obtainedusing the previously described sample preparation, metrology equipment,and the measurement conditions to provide a more accurate comparison ofenergy resolution values between different samples.

At 122 keV, the energy resolution is no greater than approximately6.40%, no greater than approximately 6.35%, no greater thanapproximately 6.30%, no greater than approximately 6.20%, no greaterthan approximately 6.10%. In a particular embodiment, at 122 keV, theenergy resolution is no greater than approximately 6.00%. At 662 keV,the energy resolution is no greater than approximately 2.90%, no greaterthan approximately 2.85%, no greater than approximately 2.80%, nogreater than approximately 2.75%, or no greater than approximately2.70%. In a particular embodiment, at 662 keV, the energy resolution isno greater than approximately 2.65%. At 2615 keV, the energy resolutionis no greater than approximately 1.90%, no greater than approximately1.85%, no greater than approximately 1.80%, no greater thanapproximately 1.75%, or no greater than approximately 1.70%. In aparticular embodiment, at 2615 keV, the energy resolution is no greaterthan approximately 1.65%.

Energy resolution ratio (“ER Ratio”) may be used to compare the energyresolutions of different compositions of materials for a particularenergy or range of energies. ER Ratio can allow for a better comparisonas opposed to energy resolution because ER Ratios can be obtained usingsubstantially the same crystal size and metrology equipment andtechniques. Thus, variations based on sample size and metrologyequipment and techniques can be substantially eliminated.

In an embodiment, the ER Ratio is the energy resolution of a particularcrystal at a particular energy or range of energies divided by theenergy resolution of another crystal at substantially the same energy orrange of energies, wherein the crystals have approximately the samesize, and the energy spectra for the crystals are obtained using thesame or substantially identical metrology equipment and techniques. Whencomparing a particular scintillation crystal having a compositiondescribed herein to a different scintillation crystal having a differentcomposition, the ER Ratio is unexpected lower, which allows for moreaccurate detection of energy peaks. When comparing the scintillationcrystals for particular energy ranges, the ER Ratio may be no greaterthan approximately 0.970 for energies in a range of 60 keV to 729 keV,no greater than approximately 0.950 for energies in a range of 122 keVto 2615 keV, no greater than approximately 0.920 for energies in a rangeof 583 keV to 2615 keV, no greater than approximately 0.900 for energiesin a range of 662 keV to 2615 keV, or any combination thereof. Whencomparing the scintillation crystals for particular energies, the ERRatio may be no greater than approximately 0.985 for an energy of 60keV, no greater than approximately 0.980 for an energy of 122 keV, nogreater than approximately 0.980 for an energy of 239 keV, no greaterthan approximately 0.970 for an energy of 511 keV, no greater thanapproximately 0.970 for an energy of 583 keV, no greater thanapproximately 0.970 for an energy of 662 keV, no greater thanapproximately 0.970 for an energy of 729 keV, or no greater thanapproximately 0.950 for an energy of 2615 keV, or any combinationthereof.

ER Ratios can be obtained for Sr-doped, Ba-doped, Mg-doped, Zn-doped,and undoped Ln(1−y)REyX3 scintillation crystals. The ER Ratios forSr-doped and Zn-doped scintillation crystals (Sr/Zn) and for Sr-dopedand undoped scintillation crystals (Sr/undoped) can meet any or all ofthe ER Ratio values for the particular energies and energy rangespreviously described. The ER Ratios for the Zn-doped and standardscintillation crystals (Zn/undoped) do not meet any of the previouslydescribed ER Ratio values for the particular energies and energy ranges.Although each of the Mg-doped and Zn-doped scintillation crystals has anER Ratio less than one, when compared to the undoped scintillationcrystal, the ER Ratio is just slightly less than 1. Thus, the Mg-dopedand Zn-doped scintillation crystals have only an insignificantimprovement regarding improved energy resolution as compared to theundoped scintillation crystal.

The scintillation crystal can have a fluorescent peak at a wavelengththat is at least approximately 20 nm greater than a wavelengthcorresponding to a fluorescent peak of a corresponding undopedscintillation crystal. In an embodiment, the Sr-doped, Ba-doped, or Srand Ba co-doped scintillation crystal has a fluorescent peak at awavelength that is a range of approximately 25 nm to approximately 50 nmgreater than a wavelength corresponding to the fluorescent peak of thecorresponding undoped scintillation crystal. In a particular embodiment,the Sr-doped, Ba-doped, or Sr and Ba co-doped scintillation crystals canhave a fluorescent peak at a wavelength in a range of approximately 375nm to approximately 380 nm, as compared to a corresponding undopedscintillation crystal (that is, a scintillation crystal consistingessentially of the same halogen(s) and rare earth element(s) as theSr-doped, Ba-doped, or Sr and Ba co-doped scintillation crystal) thathas a fluorescent peak at a wavelength in a range of approximately 355nm to approximately 360 nm. A photosensor may be more sensitive to bluelight or green light, and thus, such a photosensor can have a higherquantum efficiency for the Sr-doped, Ba-doped, or Sr and Ba co-dopedscintillation crystal as compared to the undoped scintillation crystal.

The scintillation crystal can have an energy bandgap that is at leastapproximately 0.05 eV less than a bandgap energy of a correspondingundoped scintillation crystal. In an embodiment, the scintillationcrystal can have an energy bandgap that is at least approximately 0.10eV, at least approximately 0.15 eV, or at least 0.20 eV less than thebandgap energy of the corresponding undoped scintillation crystal. In aparticular embodiment, the Sr-doped scintillation crystal has a bandgapenergy of in a range of approximately 3.26 eV to approximately 3.31 eV,and the corresponding undoped scintillation crystal has a bandgap energyof in a range of approximately 3.44 eV to approximately 3.49 eV. Ascintillation crystal with a lower bandgap energy allows morescintillating light to be produced as compared to a scintillationcrystal with higher bandgap energy for gamma rays of the same energy.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described herein. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implemented using digital circuits, and vice versa.

In a first aspect, a scintillation crystal can includeLn(1−y)REyX3:Me2+, wherein Ln represents a rare earth element, Me2+represents Sr, Ba, or any mixture thereof has a concentration of atleast approximately 0.0002 wt. %, RE represents a different rare earthelement, y has a value in a range of 0 to 1, and X represents a halogen.

In a second aspect, a radiation detection system can include ascintillation crystal including Ln(1−y)REyX3:Me+2, wherein Ln representsa rare earth element, Me+2 represents Sr, Ba, or any mixture thereof andhas a concentration of at least approximately 0.0002 wt. %, RErepresents a different rare earth element, y has a value in a range of 0to 1, and X represents a halogen. The radiation detection system canfurther include a photosensor optically coupled to the scintillationcrystal.

a scintillation crystal can include Ln(1−y)REyX3:Me2+, wherein Lnrepresents a rare earth element, RE represents a different rare earthelement, y has a value in a range of 0 to 1, X represents a halogen, andSr has a concentration of at least approximately 0.0002 wt. %.

In a second aspect, a radiation detection system can include ascintillation crystal and a photosensor optically coupled to thescintillation crystal. The scintillation crystal can includeLn(1−y)REyX3:Sr, wherein Ln represents a rare earth element; RErepresents a different rare earth element; y has a value in a range of 0to 1; X represents a halogen; and Sr has a concentration of at leastapproximately 0.0002 wt. %.

In a third aspect, a scintillation crystal can include Ln(1−y)REyX3,wherein Ln represents a rare earth element, RE represents a differentrare earth element, y has a value in a range of 0 to 1, and X representsa halogen. The scintillation crystal can have a property including, fora radiation energy range of 60 keV to 356 keV, the scintillation crystalhas an averaged value for a departure from perfect linearity of no lessthan approximately −0.35%; for a radiation energy range of 2000 keV to2600 keV, the scintillation crystal has an averaged value for adeparture from perfect linearity of no less than approximately 0.07%;for a radiation energy range of 60 keV to 356 keV, the scintillationcrystal has an absolute value for a furthest departure from perfectlinearity of no greater than approximately 0.7%; an energy resolution ofno greater than approximately 6.35% at 122 keV; an energy resolution ofno greater than approximately 2.90% at 662 keV; an energy resolution ofno greater than approximately 1.90% at 2615 keV; or any combinationthereof.

In a fourth aspect, a scintillation crystal can include Ln(1−y)REyX3,wherein, Ln represents a rare earth element, RE represents a differentrare earth element, y has a value in a range of 0 to 1, and X representsa halogen. An energy resolution ratio is an energy resolution of thescintillation crystal divided by a different energy resolution of adifferent scintillation crystal having a different composition. Theenergy resolution ratio can be no greater than approximately 0.970 forenergies in a range of 60 to 729 keV, no greater than approximately0.950 for energies in a range of 122 keV to 2615 keV, no greater thanapproximately 0.920 for energies in a range of 583 keV to 2615 keV, nogreater than approximately 0.900 for energies in a range of 662 keV to2615 keV, no greater than approximately 0.985 for an energy of 60 keV,no greater than approximately 0.980 for an energy of 122 keV, no greaterthan approximately 0.980 for an energy of 239 keV, no greater thanapproximately 0.970 for an energy of 511 keV, no greater thanapproximately 0.970 for an energy of 583 keV. no greater thanapproximately 0.970 for an energy of 662 keV, or no greater thanapproximately 0.970 for an energy of 729 keV, no greater thanapproximately 0.950 for an energy of 2615 keV, or any combinationthereof.

In a particular embodiment of any of the foregoing aspects andembodiments, the scintillation crystal has an energy resolution ratio ofno greater than approximately 0.985, no greater than approximately0.975, or no greater than approximately 0.965 for an energy of 60 keV;no greater than approximately 0.980, no greater than approximately0.950, or no greater than approximately 0.920 for an energy of 122 keV;no greater than approximately 0.990, no greater than approximately0.960, or no greater than approximately 0.940 for an energy of 239 keV;no greater than approximately 0.970, no greater than approximately0.930, or no greater than approximately 0.900 for an energy of 511 keV;no greater than approximately 0.980, no greater than approximately0.940, or no greater than approximately 0.920 for an energy of 583 keV;no greater than approximately 0.970, no greater than approximately0.910, or no greater than approximately 0.880 for an energy of 662 keV;no greater than approximately 0.970, no greater than approximately0.910, or no greater than approximately 0.880 for an energy of 729 keV;no greater than approximately 0.950, no greater than approximately0.850, or no greater than approximately 0.810 for an energy of 2615 keV;or any combination thereof.

In another particular embodiment of any of the foregoing aspects andembodiments, an energy resolution for the scintillation crystal candetermined from an energy spectrum obtained using the scintillationcrystal, a photomultiplier tube, a window disposed between thescintillation crystal and the photomultiplier tube, and a multi-channelanalyzer coupled to the photomultiplier tube. Further, the scintillationcrystal has a shape of a right circular cylinder with diameter ofapproximately 64 mm and length of approximately 75 mm, and thescintillation crystal is wrapped with a reflector on the sides and oneend, the window includes sapphire or quartz, the photomultiplier tubeincludes a linearly focused, non-saturated photomultiplier, and themulti-channel analyzer is configured to perform bi-polar shaping at a0.25 micro-s shaping time. In a more particular embodiment, the energyresolution is no greater than approximately 6.40% at 122 keV, no greaterthan approximately 2.90% at 662 keV, no greater than approximately 1.90%at 2615 keV, or any combination thereof.

In a more particular embodiment, the energy resolution is no greaterthan approximately 6.40%, no greater than approximately 6.30%, or nogreater than approximately 6.20%, no greater than approximately 6.10%,or no greater than approximately 6.00% at 122 keV. In another moreparticular embodiment, the energy resolution is no greater thanapproximately 2.90%, no greater than approximately 2.85%, no greaterthan approximately 2.80%, no greater than approximately 2.75%, nogreater than approximately 2.70% at 662 keV, or no greater thanapproximately 2.65% at 662 keV. In a further more particular embodiment,the energy resolution is no greater than approximately 1.90%, no greaterthan approximately 1.85%, no greater than approximately 1.80%, nogreater than approximately 1.75%, no greater than approximately 1.70% at2615 keV, or no greater than approximately 1.65% at 2615 keV.

In an embodiment of the first aspect, the scintillation crystal has aproperty including, for a radiation energy range of 60 keV to 356 keV,the scintillation crystal has an averaged value for a departure fromperfect linearity of no less than approximately −0.35%; for a radiationenergy range of 2000 keV to 2600 keV, the scintillation crystal has anaveraged value for a departure from perfect linearity, based on absolutevalues, of no less than approximately 0.07%; or for a radiation energyrange of 60 keV to 356 keV, the scintillation crystal has an absolutevalue for a furthest departure from perfect linearity of no greater thanapproximately 0.7%; an energy resolution of no greater thanapproximately 6.35% at 122 keV; an energy resolution of no greater thanapproximately 2.90% at 662 keV; an energy resolution of no greater thanapproximately 1.90% at 2615 keV; or any combination thereof.

In an embodiment of the second aspect, wherein the scintillation crystalhas a property including, for a radiation energy range of 60 keV to 356keV, the scintillation crystal has an averaged value for a departurefrom perfect linearity of no less than approximately −0.35%; for aradiation energy range of 2000 keV to 2600 keV, the scintillationcrystal has an averaged value for a departure from perfect linearity,based on absolute values, of no less than approximately 0.07%; for aradiation energy range of 60 keV to 356 keV, the scintillation crystalhas an absolute value for a furthest departure from perfect linearity ofno greater than approximately 0.7%; an energy resolution of no greaterthan approximately 6.35% at 122 keV; an energy resolution of no greaterthan approximately 2.90% at 662 keV; an energy resolution of no greaterthan approximately 1.90% at 2615 keV; or any combination thereof.

In a further particular embodiment of any of the foregoing aspects andembodiments, the radiation detection system is a medical imaging system.In another further particular embodiment, the scintillation crystal isdoped with Sr. In a more particular embodiment, the Sr content in thescintillation crystal is at least approximately 0.0002 wt. %, at leastapproximately 0.0005 wt. %, or at least approximately 0.001 wt. %, andin another more particular embodiment, the Sr content in thescintillation crystal is no greater than approximately 0.05 wt. %, nogreater than approximately 0.03 wt. %, no greater than 0.02 wt. %, or nogreater than approximately 0.009 wt. %.

In another particular embodiment of any of the foregoing aspects andembodiments, for a radiation energy range of 60 keV to 356 keV, thescintillation crystal has the averaged value for the departure fromperfect linearity is no less than approximately −0.35%, no less thanapproximately −0.30%, or no less than approximately −0.25%, no less thanapproximately −0.20%, or no less than approximately −0.16%. In anotherparticular embodiment, for a radiation energy range of 2000 keV to 2600keV, the scintillation crystal has the averaged value for the departurefrom perfect linearity, based on absolute values, is no greater thanapproximately 0.07%, no greater than no greater than approximately0.05%, or no greater than approximately 0.03%.

In a more particular embodiment, the averaged value for the departurefrom perfect linearity is determined by:

${DFPLaverage} = \frac{\int\limits_{E_{lower}}^{E_{upper}}{{{DFPL}\left( E_{i} \right)} \cdot \ {dE}_{i}}}{E_{upper} - E_{lower}}$

where

DFPL(Ei) is DFPL at energy Ei;

Eupper is the upper limit of the energy range; and

Elower is the lower limit of the energy range.

In yet another particular embodiment, for a radiation energy range of 60keV to 356 keV, the scintillation crystal has an absolute value for afurthest departure from perfect linearity of no greater thanapproximately 0.70%, no greater than approximately 0.65%, or no greaterthan approximately 0.60%, or no greater than approximately 0.55%, or nogreater than approximately 0.50%.

In another particular embodiment of any of the foregoing aspects andembodiments, Ln includes La, Gd, Lu, or any combination thereof. Instill another particular embodiment, RE includes Ce, Eu, Pr, Tb, Nd, orany combination thereof. In yet another particular embodiment, y is nogreater than approximately 0.5, no greater than approximately 0.2, or nogreater than approximately 0.09. In a further particular embodiment, yis at least approximately 0.005, at least approximately 0.01, or atleast approximately 0.02. In yet a further embodiment, Ln is La, RE isCe, and X is Br. In a particular embodiment y is 0.2 f.u.

In another particular embodiment of any of the foregoing aspects andembodiments, the scintillation crystal is capable of emitting a firstfluorescent peak at a first wavelength and a second fluorescent peak ata second wavelength, wherein the second wavelength is at leastapproximately 15 nm greater than the first wavelength. In a moreparticular embodiment, the second wavelength is a range of approximately20 nm to approximately 40 nm greater than the first wavelength. In afurther particular embodiment, the scintillation crystal has an energybandgap that is at least approximately 0.05 eV, at least approximately0.10 eV, at least approximately 0.15 eV, or at least 0.20 eV less than abandgap energy of a corresponding undoped scintillation crystal.

EXAMPLES

The concepts described herein will be further described in the Examples,which do not limit the scope of the invention described in the claims.The Examples demonstrate performance of scintillation crystals ofdifferent compositions. Numerical values as disclosed in this Examplessection may be approximated or rounded off for convenience.

Scintillator crystals were formed from an open crucible using LaBr3,CeBr3, and if doped, SrBr2, BaBr2, MgBr2, or ZnBr2. Because ZnBr2sublimes at approximately at approximately 700° C. at the approximatelyatmospheric pressure, incorporating the Zn into the crystal wasdifficult as the molten composition for the scintillating crystal wasmaintained at a temperature above the sublimation point of ZnBr2 duringthe slow growth stage of the REBr3 crystal, in order to form thescintillation crystal without too many crystal defects. Thescintillation crystals had the following compositions as set forth inTable 1.

TABLE 1 Standard Parameter Sr-doped Zn-doped Ba-doped Mg-doped (Undoped)or La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃ Element (%) (%) (%) (%) (%) y(f.u.) 0.05  0.05  0.05  0.05  0.05 Sr (wt. %) 0.016 — — — — Zn (wt. %)— 0.004 — — — Ba (wt. %) — — 0.025 — — Mg (wt. %) — — — 0.005 —

The scintillation crystals were analyzed for linearity, energyresolution, and band gap energy. Linearity and energy resolution wereobtained in part from energy spectral data. The scintillation crystalswere right circular cylinders with diameter of approximately 64 mm (2.5inches) and length of approximately 75 mm (3 inches). The sides and onecircular face were roughened to enhance collection of the scintillationlight. The surfaces were characterized to a root-mean-square roughnessof 0.85 microns. The other circular face of each crystal was polishedand served as the optical exit for scintillation light. The crystalswere then wrapped with approximately 0.5 mm (0.02 inches) of Teflonsheet reflector on the sides and one end. The optical exit wasinterfaced to an approximate 1.5 mm (0.06 inch) thickness of transparentsilicone rubber. The wrapped and interfaced crystal was inserted into atitanium housing with a sapphire window. The housing was welded closedand was hermetic. This crystal package was interfaced to aphotomultiplier tube (ET Enterprises Ltd. of Uxbridge, U.K., model 9305run at 900 V). The crystals response to several gamma ray emittingisotopes was measured. These isotopes included 241Am, 133Ba, 57Co,137Cs, and 228Th, which produce gamma ray photopeaks at 60, 81, 122,239, 356, 662, 583, 727, 861, 2104, and 2615 keV. The isotopes wereplaced one at a time at a distance of approximately 150 mm (6 inches)from each crystal package's midplane. The energy spectra of each isotopeand each crystal was taken using a multi-channel analyzer (CanberraIndustries Inc. of Meriden Conn., model Aptec S5008, bi-polar shaping,0.25 micro-s shaping time, 11-bit digitization).

FIGS. 2 and 3 include plots of departures from perfect linearity as afunction of gamma ray energy for the scintillation crystals havingcompositions described in Table 1. The DPFL values are determined usingthe methodology previously described. The Sr-doped scintillation crystalhas significantly less departure from perfect linearity as compared tothe Zn-doped and standard scintillation crystals.

FIG. 2 illustrates the departure from perfect linearity for gamma rayenergies in a range of approximately 200 keV to approximately 2600 keV.At energies greater than 2000 keV, the Sr-doped scintillation crystalhas a lower DFPLaverage as compared to each of the Zn-doped and standardscintillation crystals. For the energy range from approximately 2000 keVto approximately 2600 keV, the standard scintillation crystal has aDFPLaverage of +0.091%, and the Zn-doped scintillation crystal has aDFPLaverage of +0.073%. For the same energy range, the Sr-dopedscintillation crystal has the lowest DFPLaverage of +0.030%, andtherefore, the Sr-doped scintillation crystal is significantly betterthan the standard and Zn-doped scintillation crystals for the gamma rayenergies of 2000 keV to 2600 keV.

Below 1500 keV, the standard scintillation crystal has a departure fromperfect linearity that becomes significantly worse as the gamma rayenergies become smaller. The Zn-doped scintillation crystal likewise hasa significant departure but the significant departure occurs atapproximately 300 keV. For particular gamma ray energies no greater thanapproximately 356 keV, the Sr-doped scintillation crystal has adeparture from perfect linearity that is significantly closer to zero ascompared to the Zn-doped and standard scintillation crystals.

As previously discussed, the departure from perfect linearity is moresignificant at lower gamma ray energies because higher energy gamma rayscan collide with the scintillator crystal and result in lower energygamma rays. FIG. 3 includes data collected for the scintillationcrystals when exposed to gamma ray energies in a range of approximately60 keV to approximately 356 keV. The DFPLaverage is determined usingEquation 3.

TABLE 2 Energy Sr-doped Zn-doped Standard (Undoped) (keV)La_((1−y))Ce_(y)Br₃ (%) La_((1−y))Ce_(y)Br₃ (%) La_((1−y))Ce_(y)Br₃ (%)60 −0.47 −0.73 −1.11 81 −0.41 −0.65 −1.06 122 −0.26 −0.58 −0.91 239−0.10 −0.31 −0.59 356 −0.04 −0.01 −0.041 DFPL_(average) −0.16 −0.39−0.64

For the gamma energy range from approximately 60 keV to approximately356 keV, the standard scintillation crystal has a DFPL_(average) of−0.64% and the furthest DFPL is −1.11% (absolute value of 1.11%) thatoccurs at 60 keV. For the same gamma energy range, the Zn-dopedscintillation crystal has a DFPL_(average) of −0.39% and the furthestDFPL is −0.73% (absolute value of 0.73%) that occurs at 60 keV. The Srdoped scintillation crystal has a DFPL_(average) of −0.16% and thefurthest DFPL is −0.47% (absolute value of 0.47%) that occurs at 60 keV.Accordingly, the Sr-doped scintillation crystal is significantly betterand has less departure from perfect linearity as compared to each of thestandard and Zn-doped scintillation crystals. The energy resolution(“ER”) is obtained from the data collected using the samples andequipment as previously described. The energy resolution ratio (“ERRatio) is, for a particular energy or range of energies, the ratio ofthe energy resolution of a particular sample divided by the energyresolution of another sample. Table 3 includes the energy resolutiondata for undoped, Sr-doped, and Zn-doped crystals, and Table 4 includesthe energy resolution data for undoped, Ba-doped, and Mg-doped crystals.

TABLE 3 Gamma- ER of Sr- ER of Zn- ER of Ray doped doped Undoped ER ERER Energy La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃Ratio Ratio Ratio (keV) (%) (%) (%) (Sr/Zn) (Sr/Std) (Zn/Std) 60 8.608.85 8.95 0.972 0.961 0.989 122 5.98 6.41 6.51 0.933 0.919 0.985 2394.50 4.78 4.81 0.941 0.936 0.994 511 3.21 3.50 3.60 0.917 0.892 0.972583 2.89 3.10 3.15 0.932 0.917 0.984 662 2.65 2.95 3.01 0.898 0.8800.980 729 2.59 2.89 2.95 0.896 0.878 0.980 2615 1.61 1.92 2.01 0.8390.801 0.960

Additional scintillation crystals were formed and evaluated for energyresolution at 662 keV. For two additional Sr-doped scintillationcrystals, the energy resolution was 2.70% for both, and for 52additional standard scintillation crystals, the energy resolution forthe scintillation crystals was 3.02% with a standard deviation of 0.13%.

TABLE 4 Gamma- ER of Ba- ER of Mg- ER of Ray doped doped Undoped ER ERER Energy La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃ La_((1−y))Ce_(y)Br₃Ratio Ratio Ratio (keV) (%) (%) (%) (Ba/Mg) (Ba/Std) (Mg/Std) 662 2.682.70 3.01 0.898 0.880 0.980 2615 1.62 1.65 2.01 0.834 0.801 0.960

The data demonstrates that the Sr-doped and Ba-doped scintillationcrystals have significantly improved energy resolution compared to theundoped, Mg-doped, and Zn-doped scintillation crystals. Thus, Sr, Ba,and any mixture of Sr and Ba are well suited as dopants to improve theenergy resolution of rare earth halides.

FIG. 4 includes a plot of energy resolution as a function of energies ina range of 60 to 729 keV for the Sr-doped scintillation crystal, theZn-doped scintillation crystal, and the standard scintillation crystal.The Sr-doped scintillation crystal clearly has superior energyresolution as compared to the Zn-doped and undoped scintillationcrystals. The improvement in energy resolution for the Sr-dopedscintillation crystal over the standard scintillation crystal is atleast four times more than the difference between the Zn-dopedscintillation crystal and the standard scintillation crystal. Inparticular, at 122 keV, the energy resolution of the Sr-dopedscintillation crystal is 0.63% less than the energy resolution of thestandard scintillation crystal, whereas, the energy resolution of theZn-doped scintillation crystal is only 0.10% less than the energyresolution of the standard scintillation crystal. At 662 keV, the energyresolution of the Sr-doped scintillation crystal is 0.36% less than theenergy resolution of the standard scintillation crystal, whereas, theenergy resolution of the Zn-doped scintillation crystal is only 0.06%less than the energy resolution of the standard scintillation crystal.At 2615 keV, the energy resolution of the Sr-doped scintillation crystalis 0.40% less than the energy resolution of the standard scintillationcrystal, whereas, the energy resolution of the Zn-doped scintillationcrystal is only 0.09% less than the energy resolution of the standardscintillation crystal. At other energies, the Sr-doped scintillationcrystal has a lower energy resolution as compared to the Zn-dopedscintillation crystal and the standard scintillation crystal. Theimproved energy resolution means that a peak can be resolved morequickly and accurately, and can make the difference between detecting apeak and not detecting a peak, due to background noise.

Table 3 and FIG. 5 include information related to the ER Ratios whencomparing the Sr-doped scintillation crystal, the Zn-doped scintillationcrystal, and the standard scintillation crystal. Particular comparisonsare between the Sr-doped scintillation crystal and the Zn-dopedscintillation crystal, Sr-doped scintillation crystal and the standardscintillation crystal, and the Zn-doped scintillation crystal and thestandard scintillation crystal. When using an ER Ratio, a scintillationcrystal of a particular type will have better energy resolution ascompared to the other scintillation crystal. By using the ER Ratio, thecomparison between two different scintillation crystals should have lessdependence on the energy, as opposed to using only the energyresolution.

As can be seen in FIG. 5, the ER Ratio of the Sr-doped scintillationcrystal is significantly better than the Zn-doped and standardscintillation crystals. The ER Ratio for Sr/Std is 0.961 at 60 keV,decreases to 0.878 at 729 keV, and is only 0.801 at 2615 keV. Unlike theSr-doped scintillation crystal, the Zn-doped scintillation crystal isonly slightly improved as compared to the standard doped scintillationcrystal. The ER ratio for Zn/Std is nearly 1 at 239 keV and, forenergies in a range of 60 to 729 keV, only reaches 0.972 at 511 keV. Ateven high energy, such at 2615 keV, the ER ratio for Zn/Std is reachesof low of 0.960.

Data for emission spectra of the scintillation crystals were obtainedand are illustrated in FIG. 6. The Sr-doped scintillation crystal has apeak emission intensity at a wavelength in a range of 375 to 380 nm anddoes not have a significant peak at a shorter wavelength. The Zn-dopedand standard scintillation crystals have peak emission intensities at350 to 360 nm. Many photosensors have higher quantum efficiencies forblue and green light, as compared to ultraviolet radiation. Thus, theSr-doped scintillation crystal is better suited for many radiationdetectors as compared to Zn-doped and standard scintillation crystals.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Certain features that are, for clarity, described herein in the contextof separate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges includes each and every value within that range.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. A well logging apparatus comprising: ascintillation crystal including La_((i-y))RE_(y)X₃:Me²⁺, wherein: RErepresents a rare earth element other than La; y has a value in a rangeof 0 to 1; X represents a halogen; and Me²⁺ represents Sr, Ba, or anymixture thereof; and wherein the scintillation crystal has a propertyincluding: for a radiation energy range of 60 keV to 356 keV, thescintillation crystal has an average value for a departure from perfectlinearity of no less than −0.35%; for a radiation energy range of 2000keV to 2600 keV, the scintillation crystal has an average value for adeparture from perfect linearity of no greater than 0.07%; for aradiation energy range of 60 keV to 356 keV, the scintillation crystalhas an absolute value for a furthest departure from perfect linearity ofno greater than 0.7%; or any combination thereof.
 2. The well loggingapparatus of claim 1, wherein the average value for the departure fromperfect linearity (DFPL_(average)) is determined by:${{DFPL}_{average} = \frac{\int\limits_{E_{lower}}^{E_{upper}}{{{DFPL}\left( E_{i} \right)} \cdot \ {dE}_{i}}}{E_{upper} - E_{lower}}},$where DFPL(Ei) is DFPL at energy E_(i); E_(upper) is the upper limit ofthe energy range; and E_(lower) is the lower limit of the energy range.3. The well logging apparatus of claim 1, wherein the concentration ofMe²⁺ is no greater than 0.03 wt. %.
 4. The well logging apparatus ofclaim 1, wherein the concentration of Me²⁺ is in a range of 0.005 wt. %to 0.02 wt. %.
 5. The well logging apparatus of claim 1, wherein y has avalue in a range of 0.001 to 0.5.
 6. The well logging apparatus of claim1, wherein RE is Ce.
 7. The well logging apparatus of claim 1, wherein Xis Br.
 8. A medical imaging apparatus comprising: a scintillationcrystal including La_((1-y))RE_(y)X₃:Me²⁺, wherein: RE represents a rareearth element other than La; y has a value in a range of 0 to 1; Xrepresents a halogen; and Me²⁺ represents Sr, Ba, or any mixture thereofand has a concentration in a range of 0.0002 wt. % to 0.05 wt. %; aphotosensor optically coupled to the scintillation crystal; and anelectronics module coupled to the photosensor.
 9. The medical imagingapparatus of claim 8, wherein the electronics module comprises anamplifier, a pre-amplifier, a discriminator, an analog-to-digital signalconverter, a photon counter, another electronic component, or anycombination thereof.
 10. The medical imaging apparatus of claim 8,wherein the scintillation crystal has a property including: for aradiation energy range of 60 keV to 356 keV, the scintillation crystalhas an average value for a departure from perfect linearity of no lessthan −0.35%; for a radiation energy range of 2000 keV to 2600 keV, thescintillation crystal has an average value for a departure from perfectlinearity of no greater than 0.07%; for a radiation energy range of 60keV to 356 keV, the scintillation crystal has an absolute value for afurthest departure from perfect linearity of no greater than 0.7%; orany combination thereof.
 11. The medical imaging apparatus of claim 10,wherein the average value for the departure from perfect linearity(DFPL_(average)) is determined by:${{DFPL}_{average} = \frac{\int\limits_{E_{lower}}^{E_{upper}}{{{DFPL}\left( E_{i} \right)} \cdot {dE}_{i}}}{E_{upper} - E_{lower}}},$where DFPL(Ei) is DFPL at energy E_(i); E_(upper) is the upper limit ofthe energy range; and E_(lower) is the lower limit of the energy range.12. The medical imaging apparatus of claim 8, wherein RE is Ce, and X isBr.
 13. The medical imaging apparatus of claim 8, wherein the medicalimaging device is a positron emission tomography apparatus.
 14. Themedical imaging apparatus of claim 8, wherein the medical imaging deviceis a single positron emission computer tomography apparatus.
 15. Themedical imaging device of claim 8, wherein y has a value in a range of0.001 to 0.5.
 16. A security inspection apparatus comprising: ascintillation crystal including La_((1-y))RE_(y)X₃:Me²⁺, wherein: RErepresents a rare earth element other than La; y has a value in a rangeof 0 to 1; X represents a halogen; and Me²⁺ represents Sr, Ba, or anymixture thereof and has a concentration in a range of 0.0002 wt. % to0.05 wt. %.
 17. The security inspection apparatus of claim 16, whereinthe concentration of Me²⁺ is no greater than 0.03 wt. %.
 18. Thesecurity inspection apparatus of claim 16, wherein the concentration ofMe²⁺ is in a range of 0.005 wt. % to 0.02 wt. %.
 19. The securityinspection apparatus of claim 16, wherein y has a value in a range of0.001 to 0.5.